1. Field of the Invention
The present invention relates to a zoom lens system, and in particular relates to a zoom lens system suitable for a lens system having a refractive optical system (reflection member) and/or an image-stabilizing lens system.
2. Description of the Prior Art
In a zoom lens system for a compact digital camera, a positive-lead type zoom lens system and a negative-lead type zoom lens systems have been known in the art.
A positive-lead type zoom lens system can secure a larger zoom ratio without difficulty; and since the most object-side lens group thereof having a positive refractive power converges the light bundle, the diameter of subsequently lens groups can be made smaller, i.e., miniaturization of the subsequent lens groups in the radial direction is attained. However, a positive-lead type zoom lens system requires a larger number of lens elements.
On the other hand, a negative-lead type zoom lens system can reduce the number of lens elements. However, since the most object-side lens group having a negative refractive power diverges the light bundle, a negative-lead type zoom lens system is disadvantageous for miniaturization of the subsequent lens groups in the radial direction.
Furthermore, a zoom lens system can be categorized into two types: a retractable type and a fixed-length type.
In a retractable type zoom lens system, lens groups for zooming including the first (most object-side) lens group are arranged to move in the optical-axis direction with respect to the image plane when zooming is being performed; and the lens groups for zooming are also generally arranged to move in the optical-axis direction toward the image plane for the purpose of miniaturization of the camera in the camera-thickness direction when the camera is being carried (i.e., in a non-photographic state). On the other hand, a retractable type zoom lens system have the following drawbacks: (i) a longer start-up time, and (ii) slight vulnerability against waterproofing, dust proofing and shock resistance. In regard to (i), a longer start-up time is necessary, since the lens groups are moved from the retracted (non-photographic state) state to a ready-to-photograph state. In regard to (ii), due to an arrangement in which the first (most object-side) lens group is movable, the functions of waterproofing, dust proofing and shock resistance are sacrificed to some extent.
A fixed-length type zoom lens system can advantageously exhibit the functions of waterproofing, dust proofing and shock resistance, since movable lens groups for zooming are not exposed. On the other hand, the optical path length of a fixed-length type zoom lens system inevitably becomes longer. Therefore in order to attain miniaturization of a fixed-length type zoom lens system (i.e., reduce the thickness of the camera), it is known in the art to provide a reflection member (optical path bending member) such as a prism or mirror which bends the optical path within the lens system. Furthermore, such a compact (slim-bodied) camera is more difficult to hold securely, so that camera shake (image blur) easily occurs.
As explained, there are advantages and disadvantages in each of a negative-lead type zoom lens system, a positive-lead type zoom lens system, a retractable zoom lens system and a fixed-length zoom lens system. Respective type(s) is employed in accordance with requirements of size, zoom ratio, and optical performance, etc.
Moreover, it should be known that various proposals have been countlessly made nowadays in order to attain both miniaturization (e.g., a slimmer camera body) and a higher optical performance in a well balanced manner.